LEDs are not processors. One has a hard physical limit, ones does not ... at least not yet.
What is likely to be the hard limit is optical transmissivity and the heat generated from such ..... magnetic/efield optics aside of course. Even if you get super efficient LEDs, the light has to pass through or reflect off something ... and we are still talking hand-held right?
In a practical hand-held light, I would expect to top out at 90-95% total efficiency.
Let's say you can dissipate, for short periods of time, 50Watts, that means 500-1000 watts to the LED.
Let's assume 400 lumens/watt at the LED .... so 200-400,000 lumens max.
A more realistic shorter term (5-10 years) would be 75% efficiency, 50 watts thermal, and 350 lumens/watt or 70,000 lumens.
Again, talking something the size of maybe a 3 D cell flashlight.
Semiman